They called repeatedly half an hour later and left a message, I could hear typing and people in the background, then someone with a very thick accent said "Vaat da faaak" and hung up.
I suspect this is some kind of call centre. I like that the iphone allows me to just block the number permanently.

Called at 8:10pm, I didn't answer. No message was left.

I called back number (02) 8379 2350 rang 5 times then goes to busy tone.